This invention relates to a composition and a method for the manufacture of a board which is water and chemical resistant.
Various types of board are known. Examples include plywood made by gluing together sheets of wood veneer, block board made from a core of pine strip glued together with one or more sheets of wood veneer on either side of the core, chipboard or particle board formed from wood chips or particles coated with a suitable liquid adhesive such as a water based urea formaldehyde adhesive and then pressed between the heated platens of a press, and fibre board formed from wood fibres processed and pressed together to form the board. It is also known to make boards from asbestos, sisal, cellulose or other fibres, bound with Portland cement, and gypsum or calcium sulphate lined on either side with kraft paper. In the case of certain types of composite board, such as chipboard, particle board and wood fibre board, they swell when in contact with water and severe fibre lift occurs on finishing. These boards are also subject to chemical degradation, particularly in conditions of high alkalinity or acidity. Some of these boards are characterized by poor behaviour in fire or a rapid surface spread of flame. Boards made from fibre reinforced cement may have high retained alkalinity and may be characterised by high water absorbency. Further, boards made from gypsum may be degraded by water as a result of the solubility of the gypsum. There is thus a need for a new type of board which is preferably made from waste materials, which is resistant to water and chemicals, and which is relatively easy to manufacture.
U.S. Pat. No. 4,521,477 to Gunter H Kiss teaches a multilayer fibre mat which is made up of two cover layers of fibres with a high quality thermosetting plastics impregnation and making up approximately 30% of the whole mat, and a central layer of short fibre wood products with cheap thermoplastic bonding agent additives. Specifically, the central layer is made from short wood fibres bonded with an unoxidised bitumen and which also may contain a small amount of a phenolic resin. USSR Patent Specification No. 1516357 to the Leningrad Forestry Academy teaches a method of manufacturing wood fibre boards comprising the steaming of wood chips, the treatment thereof with tallow pitch in the form of a smelt at 90.degree. C. in an amount of 2.5 to 12% by weight of the chips, the grinding of the chips into fibre, the drying of the fibre, and the mixing thereof with a phenol formaldehyde resin in an amount of 3% by weight of the fibre. Subsequently, the mixture is moulded and hot pressed to form the board.